ifstream :: read不能告诉它真正读取多少字节？ [英] ifstream::read doesn't tell how many bytes it really reads?

问题描述

我使用 ifstream :: read 读取档案，

ifstream ifs("a.txt");
char buf[1024];
ifs.read(buf, 1024);

但是a.txt的大小可能小于 1000字节，所以我应该知道从 ifs ？中读取了多少字节？

But a.txt's size might be less than 1000 bytes, so how am I supposed to know how many bytes have been read from ifs?

推荐答案

您可以使用 <$ c，获取上次操作提取的字符数量$ c> std :: ifstream :: gcount ：

You can get the amount of characters extracted by the last operation with std::ifstream::gcount:

ifstream ifs("a.txt");
char buf[1024];
ifs.read(buf, 1024);
size_t extracted = ifs.gcount();

或

ifstream ifs("a.txt");
char buf[1024];
size_t extracted = ifs.read(buf, 1024).gcount();

因为 read（...） 返回 * this 。

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